1. Field of the Invention
The present invention relates to a pivot assembly bearing used for a magnetic disk drive device, for example, and in particular to a sealing structure having a sealing gap.
2. Description of the Related Art
A typical pivot assembly bearing has a structure in which a sleeve is rotatably supported around the outer circumference of the shaft through rolling bearings. A pair of rolling bearings is provided so that the rolling bearings are separated apart from each other in the axial direction. In such a pivot assembly bearing, improvements have been strongly demanded in terms of preventing emission of particles caused by leakage or evaporation of oil contained in a lubricant filled in the pivot assembly bearing. Emitted particles adhered to disk or a magnetic head causes reading and writing errors. Reducing such emission of particles thus results in a favorable influence on the lifetime and the failure rate of the magnetic disk drive device. Reducing the emission of particles from the pivot assembly bearing is demanded at a higher level in particular for the pivot assembly bearings applied to a hard disk drive device used in a server.
As measures for reducing the emission of particles, technologies have been known and disclosed in Japanese Laid-open Patent Publication No. 2006-077924 and Japanese Laid-open Patent Publication No. 2008-069920, for example. In the technologies, an annular sealing member is disposed between the shaft and the sleeve on both end portions in the axial direction, a flange integrated with the shaft is provided, and a labyrinth gap is provided between the sealing member or the flange and the rolling bearing or the shaft. Another technology has been developed in which a magnetic fluid seal is provided between the sleeve and the shaft (Japanese Laid-open Patent Publication No. 2002-027701). These measures for reducing the emission of particles also function as measures for reducing contamination of pivot assembly bearing caused by foreign materials coming from outside of bearings.
Considering the above-described measures for reducing the emission of particles, the former technology still includes a minute gap even though it is a labyrinth gap. Accordingly, the emission of particles caused by an airflow passing through the gap cannot be completely prevented. Usage of the magnetic fluid seal in the latter technology eliminates the gap where air flows because the gap is filled with a magnetic fluid. However, the magnetic fluid seal raises the cost and may require a special process in assembly.